This invention results from a need to improve octane ratings for gasoline. Isoparaffin-olefin alkylation is a means to produce highly branched paraffins which effects this octane improvement.
Alkylation is a reaction in which an alkyl group is added to an organic molecule. Thus, an isoparaffin can be reacted with an olefin to provide an isoparaffin of higher molecular weight. Industrially, the concept depends on the reaction of a C.sub.2 to C.sub.5 olefin with isobutane in the presence of an acidic catalyst producing a so-called alkylate. This is a very valuable blending component in the manufacture of gasolines because of its high octane rating.
Traditionally, the process in the industry includes the use of hydrofluoric acid or sulfuric acid and a catalysis carried out under controlled temperature conditions. Low temperatures are utilized in the sulfuric acid process to minimize the side reaction of olefin polymerization and the acid strength is generally maintained at 88 to 94% by the continuous addition of fresh acid and the continuous withdrawal of spent acid. The hydrofluoric acid process is less temperature-sensitive and the acid is easily recovered and purified.
The typical types of alkylation currently used to produce high octane blending components, that is, the hydrofluoric acid and sulfuric acid alkylation processes, have inherent drawbacks including environmental concerns, acid consumption and sludge disposal. With the increasing demands for octane and the increasing environmental concerns, it has been desirable to develop an alkylation process based on a catalyst system which can meet product quality demands, while at the same time minimizing safety and environmental problems. Studies to date indicate that Lewis acid-catalyzed alkylation processes have the potential to meet the refiners' requirements for alkylate octane and volumetric production. Examples of Lewis acids include BF.sub.3, AlCl.sub.3 and SbF.sub.5, of which BF.sub.3 presently appears to be most promising to catalyze industrial isoparaffin:olefin alkylation. The following references provide an overview of art related to BF.sub.3 -catalyzed isoparaffin-olefin alkylation.
U.S. Pat. No. 3,862,258 teaches an alkylation process using a catalyst comprising a macroreticular acid cation exchange resin and boron trifluoride. According to the patent, the life of such a catalyst can be extended by the presence in the reaction mixture of closely controlled amounts of water which can be added to the feed as water or as water-forming compound.
U.S. Pat. No. 3,450,644 discloses a method for regenerating a zeolite catalyst used in hydrocarbon conversion processes involving carbonium ion intermediates.
U.S. Pat. No. 3,549,557 describes alkylation of isobutane with C.sub.2 -C.sub.3 olefins using certain crystalline aluminosilicate zeolite catalysts in a fixed-, moving- or fluidized-bed system.
U.S. Pat. No. 3,644,565 discloses alkylation of a paraffin with an olefin in the presence of a catalyst comprising a Group VIII noble metal present on a crystalline aluminosilicate zeolite. The catalyst is pretreated with hydrogen to promote selectivity.
U.S. Pat. No. 3,647,916 describes an isoparaffin-olefin alkylation process featuring use of an ion-exchanged crystalline aluminosilicate, isoparaffin/olefin molar ratios below 3:1 and regeneration of the catalyst.
U.S. Pat. No. 3,655,813 discloses a process for alkylating C.sub.4 -C.sub.5 isoparaffins with C.sub.3 -C.sub.9 olefins using a crystalline aluminosilicate zeolite catalyst wherein a halide adjuvant is used in the alkylation reactor. The isoparaffin and olefin are introduced into the alkylation reactor at specified concentrations and catalyst is continuously regenerated outside the alkylation reactor.
U.S. Pat. No. 3,706,814 discloses another zeolite-catalyzed isoparaffin-olefin alkylation process and further provides for the addition of C.sub.5 + paraffins such as Udex raffinate or C.sub.5 +olefins to the alkylation reactor feed and the use of specific reactant proportions, halide adjuvants, etc.
U.S. Pat. No. 3,840,613 discloses a process for alkylation of paraffin hydrocarbons with olefins by reaction in the presence of a crystalline aluminosilicate zeolite catalyst activated by the sequential steps of ion exchange, steaming, reexchange and calcination.
U.S. Pat. No. 3,624,173 discloses an isoparaffin-olefin alkylation which uses crystalline aluminosilicate zeolites containing gallium.
U.S Pat. No. 3,738,977 discloses alkylation of paraffins with ethylene using a zeolite catalyst which possesses a Group VII metal component. The catalyst is pretreated with hydrogen.
U.S. Pat. No. 3,917,738 describes a process for alkylating an isoparaffin with an olefin using a solid, particulate catalyst capable of absorbing the olefin. The isoparaffin and the olefin are admixed to form a reactant stream in contact with catalyst particles at the upstream end of an adsorption zone. Thereafter, the reactants are passed concurrently with the catalyst so that a controlled amount of olefin is adsorbed into the catalyst before the combination of reactants and catalyst is introduced into an alkylation zone. This controlled olefin adsorption is thought to prevent polymerization of the olefin during alkyation.
U.S. Pat. No. 4,384,161 describes a process of alkylating isoparaffins with olefins to provide alkylate using a large-pore zeolite catalyst capable of absorbing 2,2,4-trimethylpentane, for example, ZSM-4, ZSM-20, ZSM-3, ZSM-18, zeolite Beta, faujasite, mordenite, zeolite Y and the rare earth metal-containing forms thereof, and a Lewis acid such as boron trifluoride, antimony pentafluoride or aluminum trichloride. The use of a large-pore zeolite with a Lewis acid is reported to increase the activity and selectivity of the zeolite, thereby effecting alkylation with high olefin space velocity and low isoparaffin/olefin ratio.
The article entitled "Fixed Bed Catalytic Process to Product Synthetic Lubricants from Decene-1", Ind. Eng. Chem. Prod. Res. Dev., 22, (1983), teaches oligomerizing olefins to produce fluids with lubricating properties using a silica-BF.sub.3 -water catalyst The authors further teach that with this system much of the BF.sub.3 can be recycled to minimize BF.sub.3 consumption and disposal problems The reference teaches that water is a necessary component of the system and that in its absence a BF.sub.3 -silica catalyst rapidly deactivates. The reference further teaches that for less reactive olefins, such as decene-1, a useful degree of oligomerization is achieved only by adding a measurable quantity of an activator such as water or a primary alcohol to BF.sub.3. The authors further point out that other BF.sub.3 activators, such as ethers, ketones, acids and anhydrides, are also effective olefin oligomerization catalysts A commercialized process is reported wherein alkylation of benzene with ethylene, propylene or butenes is achieved by using a BF.sub.3 -alumina catalyst with BF continually added to the feedstock. The article states that the process minimizes both BF.sub.3 consumption and disposal problems and further provides a product having excellent lubricating properties. The catalyst is said to require water as an activator.
In U.S. Pat. No. 4,308,414 an olefin, such as 1-decene, is oligomerized in the presence of a three-component catalyst comprising boron trichloride, a minute amount of water and a particulate absorbent material such as silica to a lubricating product predominating in those oligomer fractions having viscosities within the lubricating oil range such as the trimer and tetramer.
U.S. Pat. No. 4,429,177 further relates to a method for making lubricating oil utilizing a catalyst comprising boron trifluoride, a minute amount of elemental oxygen and a particulate absorbent material such as silica. The reference points out that the two-component catalyst comprising a solid absorbent and boron trifluoride gradually loses activity after a period of continued use, which aging cannot be conveniently corrected by increasing the boron trifluoride pressure. As a solution, the reference teaches that this aging can be essentially prevented if a minute amount of elemental oxygen is fed to the reactor.
U.S. Pat. No. 3,997,621 relates to oligomerization of olefins catalyzed by boron trifluoride which is controlled to yield desired trimer as a dominant lubricant product by adding small amounts of ester together with water or alcohol promoter.
U.S. Pat. No. 4,365,105 also relates to oligomerizing an olefin to form lubricating oils in the presence of three-component catalyst which comprises a particular silica absorbent with boron trifluoride and water absorbed on the silica.
U.S. Pat. No. 2,804,491 relates to an isoparaffin/olefin alkylation to make gasoline at temperatures between -20 and 150.degree. F. utilizing a two-component catalyst comprising essentially excess BF.sub.3 with a "silica stabilized gel alumina". No activators are taught.
In the past, severe activity and stability problems have been noted with respect to zeolite based systems. U.S. Pat. Nos. 3,251,902 and 3,893,942, as well as French Patent 1,593,716, and the article by Kirsh and Potts, Div. of Pet. Chem. A.C.S.. 15, A109 (1970), exemplify these problems. Improved stability was noted when a Lewis acid such as BF.sub.3 was used in combination with macroreticular acid cation exchange resins as pointed out in U.S. Pat. No. 3,855,342. More recently, U.S. Pat. No. 4,384,161 has disclosed the use of BF in combination with large pore zeolites such as ZSM-4 and Beta to effectively catalyze isoparaffin/olefin alkylation reactions.
U.S. Pat. No. 3,467,728 relates to a process for isomerizing olefinic hydrocarbon, such as 1-butene or 1-pentene, by contacting the hydrocarbon with a catalyst comprising a crystalline alumina silicate combined with a substantially anhydrous boron halide.
U.S. Pat. No. 3,800,003 relates to a process for producing an alkylation reaction product from an isoparaffinic reactant and an olefinic reactant containing 1-butene, 2-butene and isobutene which includes passing the olefinic reactant through an isomerization zone. The isomerization catalyst comprises a crystalline aluminosilicate combined with a substantially anhydrous boron halide which can be boron trifluoride. Conventional catalysts are utilized for the alkylation reaction and include sulfuric acid and hydrogen fluoride catalyst which have the disadvantages set forth above.
The problem of acid consumption remains as an obstacle to commercialization of Lewis acid catalyzed alkylation, first because of the high cost of suitable Lewis acids, and second because of the cost of disposing of an acid neutralization byproduct if the acid is not recycled. Specifically, it would be highly beneficial to provide a process which efficiently separates and recycles the Lewis acid component of the alkylation catalyst to the alkylation reaction zone while avoiding the capital and operating costs associated with a Lewis acid/light aliphatic fractionation section. For example, in a typical BF.sub.3 -catalyzed isobutane:2-butene alkylation process employing feeds contianing minor amounts of lighter hydrocarbons, the reactor effluent product is first fractionated to separate C.sub.4 - components from C.sub.5 + alkylate. The overhead stream from this fractionation step typically contains not only BF.sub.3 but also unreacted propane which must be removed before the BF.sub.3 is recycled to the alkylation reactor. While the two components are separable by distillation, their close boiling points require a tall, expensive distillation tower. Further, the tower must be constructed with a nickel-rich alloy such as Monel to resist corrosive attack by the BF.sub.3.
U.S. Pat. No. 4,384,162 to Vogel teaches a method of removing BF.sub.3 from organic liquids by passing the organic liquid through a bed of granular polyvinyl alcohol (PVA). When the PVA adsorbent is saturated with BF.sub.3, it is taken out of service for extraction of BF.sub.3 from the PVA. This BF.sub.3 recovery step is accomplished by heating the PVA to a temperature of about 100.degree. C. to vaporize off the BF.sub.3, or alternatively, contacting the PVA with a polar solvent to desorb BF.sub.3. Unfortunately, neither of these regeneration techniques lends itself to continuous BF.sub.3 recovery in conjunction with a BF.sub.3 alkylation process. Heating the sorbent to vaporize BF.sub.3 necessarily requires handling a recycle stream enriched in BF.sub.3 , an option complicated by numerous environmental and safety precautions. On the other hand, while dissolving the BF.sub.3 from the PVA with a polar solvent would seem to eliminate the safety and environmental hazards associated with handling a gaseous BF.sub.3 stream, the BF.sub.3 must be separated from the polar solvent before recycling BF.sub.3 to the alkylation reaction zone. Thus, it would be highly beneficial if a Lewis acid sorption process could be developed which could be readily integrated into a continuous alkylation scheme without the hazards associated with handling purified Lewis acids.
The alkylate gasoline produced by the processes discussed above is not only characteristically free from impurities such as sulfur, but is also low in aromatics. With the advent of increasingly stringent regulations restricting the content of motor gasolines, demand for such alkylate gasolines will continue to increase. To meet the market requirements for alkylate gasoline octane quality while promoting safe refinery operation and minimizing environmental risks, it would be highly desirable to provide a Lewis acid catalyzed isoparaffin:olefin alkylation process for the production of motor gasoline blending stock which process minimizes Lewis acid catalyst consumption by recovering and recycling the Lewis acid catalyst from the product stream without handling concentrated Lewis acid, and without the capital and operating costs associated with Lewis acid/C.sub.3 - hydrocarbon distillation.
Each of the preceeding references is incorporated by reference as if set forth at length herein